1. Field of the Invention:
The present invention relates to a fail-safe method and apparatus for internal combustion engines for motor vehicles.
2. Description of the Prior Art:
Control devices for fuel injection apparatus for engines of motor vehicles are known in the prior art in which intake air flow and engine speed are detected and, from the detected values of the intake air flow and the engine speed, a basic injection time is determined to control the amount of fuel to be injected from an injection valve (L-EFI). Alternatively, control devices are known in which an intake air pressure on the downstream side of a throttle valve and engine speed are detected and, from the detected values of the intake air pressure and the engine speed, a basic injection time is determined to control the amount of fuel to be injected from an injection valve (D-EFI).
In D-EFI, where the amount of fuel to be injected is controlled on the basis of the intake air pressure and the engine speed, if an intake pipe downstream of the throttle valve is broken or leaks, a large amount of fuel will be injected because the intake air pressure detected increases to atmospheric pressure. Therefore, since air is supplied into the engine through the broken part without being throttled by the throttle valve, the engine speed tends to rise excessively high.
An apparatus for detecting an abnormal value of the measured intake air pressure (indicative of a problem with the intake system) is disclosed in Japanese Patent Provisional Publication (Kokai) No. 57-52643. This document teaches comparing a detected value of intake pressure to throttle valve position and judging an abnormality when the detected pressure exceeds a limit when the throttle valve is closed.